1. Field of the Present Invention
The present invention relates to a display device, and particularly to a display device and a thin film transistor array substrate and a thin film transistor thereof with low current leakage.
2. Description of the Related Art
Reflective display device shows images by using the reflected incident light as light source. Since the back light source is unnecessary for the reflective display device, the power-consumption and the size of the reflective display device can be reduced. Therefore, the reflective display device is taken highly attention in recently display device markets.
Further, the display devices of nowadays mostly can be grouped into active display devices and passive display devices according to driving elements thereof. Usually, active display devices use thin film transistors as driving elements. Moreover, since amorphous silicon thin film transistor (a-Si TFT) has the advantages of low cost and simple production, mostly active display devices use amorphous silicon thin film transistors as driving elements.
FIG. 1 is a schematic cross-section view of thin film transistor array substrate in single pixel of the conventional active display device. Referring to FIG. 1, a gate electrode 104 is formed on the substrate 102 firstly during the process of the thin film transistor array substrate 100. Next, a gate insulating layer 106 is formed to cover the gate electrode 104. Then, an amorphous silicon layer (not shown in FIG. 1) is formed on the gate insulating layer 106. Since the amorphous silicon layer is opaque, the amorphous silicon layer is then removed except the portion located above the gate electrode 104 for increasing aperture ratio of the pixel. Therefore, the non-removed portion of the amorphous silicon layer is regarded as a channel layer 108.
Then, a source electrode 110 and a drain electrode 112 are formed on the gate insulating layer 106 to cover a portion of the channel layer 108. At this time, the manufacturing process of a thin film transistor 101 is substantially finished. Next, a protective layer 114 with opening 116 is formed on the substrate 102. A portion of the drain electrode 112 is exposed by the opening 116. Then, a pixel electrode 118 is formed on the protective layer 114 and filled into the opening 116. Thus, the pixel electrode 118 is electrically connected to the drain electrode 112.
However, since the amorphous silicon materials have optical-electric properties, if the thin film transistors array 100 is used in reflective display device, when the light emitted from environment illuminates the channel layer 108, current leakage is generated in the channel layer 108, so that the action of the thin film transistor may be unusual and resulted in abnormal display of the display device.
A conventional method is provided for preventing the light emitted from environment from illuminating the channel layer 108 by forming a metal light-shielding layer (not shown in FIG. 1) on the channel layer 108. Thus, the current leakage may be prevented from being generated. However, forming the metal light-shielding layer may increase the cost of the reflective display device.